1. Field of the Invention
This invention relates to a thermal ink jet printhead design and method of manufacture and, more particularly, to an improved method of fabricating a thermal ink jet printhead by dicing the nozzle face after photodelineating the thick film layer in the ink channels downstream from the heating elements to form a printhead with a stepped nozzle face that allows more effective cleaning and improved droplet directionality.
A concurrently filed application, U.S. Ser. No. 07/577,245, filed Sept. 4, 1990, by the same inventor and assignee entitled "Thermal Ink Jet Printhead with Pre-Diced Nozzle Face and Method of Fabrication Therefor" discloses a related invention.
2. Description of the Prior Art
Thermal ink jet printing, though capable of continuous stream operation, is generally a type of drop-on-demand ink jet systems, wherein an ink jet printhead expels ink droplets on demand by the selective application of a current pulse to a thermal energy generator, usually a resistor, located in capillary-filled, parallel ink channels a predetermined distance upstream from the channel nozzles or orifices. The channel end opposite the nozzles are in communication with a small ink reservoir to which a larger external ink supply is connected.
U.S. Pat. No. Re. 32,572 to Hawkins et al discloses a thermal ink jet printhead and several fabricating processes therefor. Each printhead is composed of two parts aligned and bonded together. One part is a substantially flat substrate which contains on the surface thereof a linear array of heating elements and addressing electrodes, and the second part is a substrate having at least one recess anisotropically etched therein to serve as an ink supply manifold when the two parts are bonded together. A linear array of parallel grooves are also formed in the second part, so that one end of the grooves communicate with the manifold recess and the other ends are open for use as ink droplet expelling nozzles. Many printheads can be made simultaneously by producing a plurality of sets of heating element arrays with their addressing electrodes on a silicon wafer and by placing alignment marks thereon at predetermined locations. A corresponding plurality of sets of channel grooves and associated manifolds are produced in a second silicon wafer. In one embodiment, alignment openings are etched in the second silicon wafer at predetermined locations. The two wafers are aligned via the alignment openings and alignment marks, then bonded together and diced into many separate printheads.
U.S. Pat. No. 4,638,337 to Torpey et al discloses an improved thermal ink jet printhead similar to that of Hawkins et al, but has each of its heating elements located in a recess. The recess walls containing the heating elements prevent the lateral movement of the bubbles through the nozzle and therefore the sudden release of vaporized ink to the atmosphere, known as blow-out, which causes ingestion of air and interrupts the printhead operation whenever this event occurs. In this patent, a thick film organic structure such as Riston.RTM. or Vacrel.RTM. is interposed between the heater plate and the channel plate. The purpose of this layer is to have recesses formed therein directly above the heating elements to contain the bubble which is formed over the heating elements, thus enabling an increase in the droplet velocity without the occurrence of vapor blow-out and concomitant air ingestion.
U.S. Pat. No. 4,774,530 to Hawkins discloses an improvement over the above-mentioned patent to Torpey et al. Recesses are also patterned in the thick film layer to provide a flow path for the ink from the manifold to the channels by enabling the ink to flow around the closed ends of the channels, thereby eliminating the fabrication steps required to open the groove closed ends to the manifold recess, so that the printed fabrication process is simplified.
U.S. Pat. No. 4,878,992 to Campanelli discloses an ink jet printhead fabrication process wherein a plurality of printheads are produced from two mated substrates by two dicing operations. One dicing operation produces the nozzle face for each of a plurality of printheads and optionally produces the nozzles. This dicing blade, together with specific operating parameters, prevent the nozzles from chipping and the nozzle faces from scratches and abrasions. A second dicing operation with a standard dicing blade severs the mated substrates into separate printheads. The dicing operation which produces the nozzle face is preferably conducted in a two-step operation. A first cut makes the nozzle face, but does not sever the two mated substrates. A second dicing cut severs the two substrates, but does so in a manner that prevents contact by the dicing blade with the nozzle face.
In the above patents and in other prior art fabrication methods, the nozzle face of the printheads were made by either a separately fabricated nozzle plate which contains the nozzles and is bonded to the printheads, photolithographically produced from laminated layers, or dicing operation in which aligned and bonded channel plates and heating element plates having a patterned thick film layer sandwiched therebetween are concurrently cut. Unfortunately, in the latter method, the thick film layer cannot consistently be cut in a reliable way. Sometimes a burr is left which causes misdirection of an ejected droplet and, thus poor image quality. In addition, the dicing blade is considerably worn when it cuts non-silicon material, such as, when sectioning the heating element and channel wafers and sandwiched intermediate thick film layer as taught by U.S. Pat. No. 4,878,992.
The invention overcomes the disadvantages of the prior art fabrication methods, eliminating a host of defects which affect dicing yield, and reduces dicing blade wear by orders of magnitude.